Appliance with coated transparency

ABSTRACT

An appliance transparency, such as an oven transparency, includes at least one substrate and a coating deposited over at least a portion of the substrate. The coating includes at least one metal layer, such as a metallic silver layer. The metal layer can have a thickness in the range of 80 Å to 100 Å and optionally or the coating can have a protective coating deposited thereon.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims the benefits of U.S. ProvisionalApplication No. 60/474,813 filed May 30, 2003, and U.S. ProvisionalApplication No. 60/502,784 filed Sep. 12, 2003, both of whichapplications are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to transparencies, such as butnot limited to transparencies for furnaces, conventional ovens,microwave ovens, convection-microwave ovens, self-cleaning ovens,refrigerators, fireplaces, and the like. In one particular aspect, thisinvention relates to a coated panel for use in an appliance transparencyand to appliance transparencies incorporating at least one such coatedpanel.

[0004] 2. Description of the Currently Available Technology

[0005] Appliances, such as furnaces, conventional ovens, microwaveovens, convection-microwave ovens, self-cleaning ovens, andrefrigerators, just to name a few, often have a transparency throughwhich material inside the appliance can be viewed. These appliancetransparencies also typically have heat or radiation reflecting elementsto reduce heat or radiation passing through the transparency.

[0006] For example, conventional oven doors typically have atransparency formed by three or four spaced glass sheets. The glasssheets are typically about 5 mm thick. The two inner sheets (closest tothe oven interior) have heat reflective coatings on both their inner andouter surfaces to reduce heat from the interior of the oven escapinginto the ambient atmosphere. For example, it is known to provide aconventional oven door transparency in which the inner and outersurfaces (the No. 1 and No. 2 surfaces) of the innermost sheet and alsothe inner and outer surfaces (the No. 3 and No. 4 surfaces) of theadjacent sheet are coated with a heat reflective fluorine-doped tinoxide coating. Conventionally, for ovens the No. 1 surface is defined asthe innermost surface (i.e., the surface closest to the heat source) andthe other surfaces are numbered consecutively by counting outwardly fromthe No. 1 surface. This fluorine-doped tin oxide coating is typicallyapplied to the glass sheets by spray pyrolysis. While adequate for heatreflection, this conventional appliance transparency structure does havesome drawbacks. For example, spray pyrolysis of the fluorine-doped tinoxide coatings can result in uneven coating thickness across the surfaceof the sheet. This uneven coating thickness can lead to color andreflectance variations in the coated sheet that can be aestheticallyundesirable. Additionally, this conventional oven transparency structurerequires the application of four separate coatings (one coating on eachside of the inner two sheets).

[0007] Conventional “self-cleaning oven” doors are similar toconventional oven doors but must meet certain industry recognized safetystandards, such as a maximum permissible outer temperature duringcleaning, in order to be sold in the United States. In order to meetthese standards, conventional self-cleaning oven doors typically have avent system to allow for convective flow of ambient air through the doorto help carry away heat to decrease the temperature of the outer doorduring the cleaning cycle. However, this convective flow of ambient airintroduces heated air into the kitchen and can increase the ambienttemperature in the kitchen, making the kitchen uncomfortable to work in.

[0008] Conventional microwave oven doors are typically formed by aninner polymeric panel (such as a Mylar® sheet), an intermediate wiremesh grid, and an outer glass sheet. The inner Mylar® panel providesease of cleaning and the intermediate wire mesh grid prevents microwaveradiation from the interior of the oven passing through thetransparency. Again, while adequate for its intended purposes, thisconventional microwave oven door structure does have some drawbacks. Forexample, the conventional microwave oven door requires three separatepieces that must be assembled in order for the door to functionproperly. Moreover, it may be difficult to adequately view materialinside the oven through the wire mesh grid.

[0009] Therefore, it would be advantageous to provide a coated sheet orpanel that can be utilized in appliance transparencies that reduces oreliminates at least some of the drawbacks described above. For example,it would be advantageous to provide a conventional oven door in whichfewer than four coatings were needed to provide acceptable performance.It would be advantageous to provide an oven door, such as aself-cleaning oven door, in which the conventional vent system can bereduced or eliminated while still meeting the recognized safetystandards. Additionally, it would be advantageous to provide a microwaveoven transparency that eliminates at least some of the requiredcomponents of conventional microwave oven transparencies and/or providesincreased visibility through the microwave oven transparency.

SUMMARY OF THE INVENTION

[0010] An appliance transparency comprises at least one substrate. Atleast one first coating is deposited over at least a portion of thesubstrate. The at least one first coating can comprise at least onemetal layer having a thickness in the range of 80 Å to 100 Å and/or aprotective coating. The transparency can further include a secondcoating comprising a metal layer having a thickness in the range of 80 Åto 100 Å and/or a protective coating. In one embodiment, the substrateincludes a first surface and a second surface with the first coatingformed over at least a portion of the first surface and the secondcoating formed over at least a portion of the second surface. In aparticular embodiment, the first and second coatings can each includemore than one metal layer. For example, the first coating can includeone or more, e.g., three, metallic silver layers and the second coatingcan include one or more, e.g., three, metallic silver layers. At leastone of the first and second coatings can include a protective coating.Alternatively, one or more of the coatings can be a metal oxide coatingfree of any metal layers.

[0011] An oven transparency comprises a first panel defining a No. 1 anda No. 2 surface, a second panel spaced from the first panel and defininga No. 3 and a No. 4 surface, optionally a third panel spaced from thesecond panel and defining a No. 5 and a No. 6 surface, and optionally afourth panel defining a No. 7 and a No. 8 surface. At least one coatingis formed over at least a portion of at least one of the panels. The atleast one coating can comprise at least one metal layer. In oneembodiment, the oven transparency includes a first coating formed overat least a portion of one surface, e.g. the No. 3 surface, and a secondcoating formed over at least a portion of a second surface, e.g. the No.5 and/or No. 6 surfaces. The first and second coatings can each includeat least one metal layer. For example, the first coating can include oneor more, e.g., three, metallic silver layers and the second coating caninclude one or more, e.g., three, metallic silver layers. At least oneof the first and second coatings can include a protective overcoat.

[0012] An oven transparency comprises a composite panel comprising afirst sheet adjacent, e.g., contacting, a second sheet. At least one ofthe surfaces of at least one of the sheets can include a heat and/orradiation reflecting coating. In one particular embodiment, the oventransparency comprises a first panel defining a No. 1 and a No. 2surface, a second panel defining a No. 3 and a No. 4 surface, andoptionally a third panel defining a No. 5 and a No. 6 surface. At leastone panel is a composite panel comprising a first glass sheet contactinga second glass sheet.

[0013] A microwave oven transparency comprises a first panel and atleast one coating formed over at least a portion of the first panel. Theat least one coating can comprise at least one metal layer. For example,the at least one coating can include one or more, e.g., three, metallicsilver layers. An optional polymeric layer, such as a polymeric coatingor a polymeric sheet, can be provided over or adjacent to the at leastone coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view (not to scale) of an exemplaryappliance in the form of an oven incorporating features of theinvention;

[0015]FIG. 2 is a partial sectional view (not to scale) of an oven doorhaving a transparency incorporating features of the invention;

[0016]FIG. 3 is a side, sectional view (not to scale) of a coated panelof the invention useful for forming an appliance transparency;

[0017]FIG. 4 is a partial sectional view (not to scale) of an exemplarymicrowave oven door having a transparency incorporating features of theinvention;

[0018]FIG. 5 is a side, sectional view (not to scale) of another coatedpanel of the invention useful for forming an appliance transparency;

[0019]FIG. 6 is a partial sectional view (not to scale) of aconvection-microwave oven door having a transparency incorporatingfeatures of the invention;

[0020]FIG. 7 is a side, sectional view (not to scale) of a self-cleaningoven door incorporating features of the invention;

[0021]FIG. 8 is a side, sectional view (not to scale) of another ovendoor incorporating features of the invention;

[0022]FIG. 9 is a side, sectional view (not to scale) of a further ovendoor incorporating features of the invention; and

[0023]FIG. 10 is a side, sectional view (not to scale) of an additionaloven door incorporating features of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] As used herein, spatial or directional terms, such as “left”,“right”, “inner”, “outer”, “above”, “below”, and the like, relate to theinvention as it is shown in the drawing figures. However, it is to beunderstood that the invention can assume various alternativeorientations and, accordingly, such terms are not to be considered aslimiting. Further, as used herein, all numbers expressing dimensions,physical characteristics, processing parameters, quantities ofingredients, reaction conditions, and the like, used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical values set forth in the following specificationand claims may vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical value should at least be construedin light of the number of reported significant digits and by applyingordinary rounding techniques. Moreover, all ranges disclosed herein areto be understood to encompass the beginning and ending range values andany and all subranges subsumed therein. For example, a stated range of“1 to 10” should be considered to include any and all subranges between(and inclusive of) the minimum value of 1 and the maximum value of 10;that is, all subranges beginning with a minimum value of 1 or more andending with a maximum value of 10 or less, e.g., 5.5 to 10. Further, asused herein, the terms “formed over”, “deposited over”, or “providedover” mean formed, deposited, or provided on but not necessarily incontact with the surface. For example, a coating layer “formed over” asubstrate does not preclude the presence of one or more other coatinglayers or films of the same or different composition located between theformed coating layer and the substrate. All documents referred to hereinare to be understood to be incorporated by reference in their entirety.As used herein, the terms “polymer” or “polymeric” refer to oligomers,homopolymers, copolymers, and terpolymers, e.g., polymers formed fromtwo or more types of monomers or polymers. The terms “visible region” or“visible light” refer to electromagnetic radiation having a wavelengthin the range of 380 nm to 780 nm. The terms “infrared region” or“infrared radiation” refer to electromagnetic radiation having awavelength in the range of greater than 780 nm to 100,000 nm. The terms“ultraviolet region” or “ultraviolet radiation” mean electromagneticenergy having a wavelength in the range of 300 nm to less than 380 nm.The terms “microwave region” or “microwave radiation” refer toelectromagnetic radiation having a frequency in the range of 300megahertz to 300 gigahertz.

[0025] The invention will first be described with reference to use in atransparency for a conventional oven door and then with reference totransparencies for conventional microwave ovens, conventionalconvection-microwave ovens, and conventional self-cleaning ovens.However, it is to be understood that these are simply exemplary uses ofthe invention and that the invention is not limited to theseparticularly disclosed examples. Moreover, the invention need not belimited to use with appliance transparencies but could be utilized forother articles, such as but not limited to vehicle transparencies suchas automotive windshields, sidelights, back lights, moon roofs, sunroofs, aviation transparencies, boat or other marine transparencies,refrigerator doors, skylights, and fireplace screens, just to name afew. The invention can be practiced with laminated or monolithicarticles. By “monolithic” is meant having a single structural ply.Additionally, while a typical appliance or vehicle “transparency” canhave sufficient visible light transmittance such that materials can beviewed through the transparency, in the practice of the invention the“transparency” need not be transparent to visible light but could betranslucent or opaque (as described below).

[0026] An exemplary appliance in the form of an oven 10 is shown inFIG. 1. Since the structure and operation of conventional-ovens(including self-cleaning ovens and microwave ovens) will be wellunderstood by those of ordinary skill in the art, a detailed descriptionwill not be provided. The oven 10 includes a body 12 having an interiorcooking chamber 14. An access, e.g., a hinged oven door 16, providesaccess to the cooking chamber 14. A transparency 18 can be provided,e.g., in the oven door 16, such that when the door 16 is closed,material in the cooking chamber 14 can be viewed. The cooking chamber 14typically includes one or more heat sources 20. In a conventional oven,the heat source 20 typically includes electrically heated metal grids orgas burners. In a microwave oven, the heat source 20 typically includesone or more radiation sources, e.g., microwave radiation sources. Forconvection-microwave ovens, the heat sources 20 can include bothelectrically heated grids and microwave radiation sources. Inconventional self-cleaning ovens, the door 16 typically includes aplurality of top vents 150 and a plurality of bottom vents (not shown)that allow for convective flow of ambient air through the door 16 asdescribed in more detail below.

[0027] Use of the invention with a conventional oven transparency willfirst be described. As discussed above, conventional oven transparenciestypically are formed by three or four spaced glass sheets havingfluorine-doped tin oxide coatings on the inner and outer surfaces of thetwo inner glass sheets (i.e., a total of four coated surfaces). However,an exemplary oven door 24 having a transparency 26 incorporatingfeatures of the invention is shown in FIG. 2. The transparency 26includes at least one sheet or panel having at least one coatingincorporating features of the invention. The at least one coating canhave at least one metal layer. In the exemplary embodiment shown in FIG.2, the transparency 26 includes three spaced panels 30, 32, 34 held in aconventional spacer assembly in any conventional manner. However, it isto be understood that the invention is not limited to use with threepanels but could be used with four or more panels. The first or innerpanel 30 (closest to the interior of the cooking chamber 14) has aninner surface 36 (No. 1 surface) facing the chamber 14 and an outersurface 38 (No. 2 surface). The second or middle panel 32 is spaced fromthe first panel 30 by the spacer assembly and includes an inner surface40 (No. 3 surface) and an outer surface 42 (No. 4 surface). The third orouter panel 34 is spaced from the second panel 32 and includes an innersurface 44 (No. 5 surface) and an outer surface 46 (No. 6 surface).Although not shown, the transparency 26 could include a fourth panelspaced outwardly from the third panel 34. The exemplary transparency 26includes at least one first coating 50 formed over at least a portion ofone of the panel surfaces and at least one second coating 52 formed overat least a portion of another surface. In the illustrated exemplarytransparency 26, the first coating 50 is shown formed over the No. 1surface 36 and the second coating 52 is shown formed over the No. 3surface 40. However, it is to be understood that the first and secondcoatings 50, 52 need not be limited to these positions. The first andsecond coatings 50, 52 could be provided on any of the surfaces. Forexample but not limiting to the invention, the first coating 50 could belocated on the No. 4 surface 42 as shown by the dashed line in FIG. 2and the second coating 52 on the No. 3 surface 40. Alternatively, thefirst coating 50 could be located on the No. 3 surface and the secondcoating 52 on the No. 4 surface or the No. 5 surface.

[0028] A first air gap 152 is defined between the first and secondpanels 30, 32 and a second air gap 154 is defined between the second andthird panels 32, 34. As described above, conventional “self-cleaningoven” doors typically include a plurality of bottom vents 156 and aplurality of top vents 150. However, as described in more detail below,in one practice of the invention, these vents 150, 156 can besignificantly reduced in dimension or eliminated all together.

[0029] In the broad practice of the invention, the panels 30, 32, 34 ofthe transparency 26 can be of the same or different materials. Thepanels can include any desired material having any desiredcharacteristics. For example, one or more of the panels can betransparent, translucent, or opaque to visible light. By “transparent”is meant having visible light transmittance of greater than 0% to 100%.Alternatively, one or more of the panels can be translucent or opaque.By “translucent” is meant allowing electromagnetic energy (e.g., visiblelight) to pass through but diffusing this energy such that objects onthe side opposite the viewer are not clearly visible. By “opaque” ismeant having a visible light transmittance of 0%. Examples of suitablematerials include, but are not limited to, plastic substrates (such asacrylic polymers, such as polyacrylates; polyalkylmethacrylates, such aspolymethylmethacrylates, polyethylmethacrylates,polypropylmethacrylates, and the like; polyurethanes; polycarbonates;polyalkylterephthalates, such as polyethyleneterephthalate (PET),polypropyleneterephthalates, polybutyleneterephthalates, and the like;polysiloxane-containing polymers; or copolymers of any monomers forpreparing these, or any mixtures thereof); metal substrates, such as butnot limited to galvanized steel, stainless steel, and aluminum; ceramicsubstrates; tile substrates; glass substrates; or mixtures orcombinations of any of the above. For example, one or more of the panelscan include conventional untinted soda-lime-silica glass, i.e., “clearglass”, or can include tinted or otherwise colored glass, borosilicateglass, leaded glass, tempered, untempered, annealed, orheat-strengthened glass. The glass may be of any type, such asconventional float glass or flat glass, and may be of any compositionhaving any optical properties, e.g., any value of visible radiationtransmission, ultraviolet radiation transmission, infrared radiationtransmission, microwave energy transmission, and/or total solar energytransmission. Types of glass suitable for the practice of the inventionare described in, but are not limited to, U.S. Pat. Nos. 4,746,347;4,792,536; 5,240,886; 5,385,872; and 5,393,593. Further, one or more ofthe panels can include a plastic and/or polymeric substrate with acoating of the invention deposited on the polymeric substrate's surface.

[0030] The first coating 50 can be a heat and/or radiation reflectingcoating and can have one or more functional coating layers or films ofthe same or different composition and/or functionality. As used herein,the term “film” refers to a coating region of a desired or selectedcoating composition. A “layer” can comprise one or more “films” and a“coating” or “coating stack” can comprise one or more “layers”. Forexample, the first coating 50 can be a single layer coating or amulti-layer coating and can include one or more metals, non-metals,semi-metals, semiconductors, and/or alloys, compounds, compositions,combinations, or blends thereof. For example, the first coating 50 canbe a single layer metal oxide coating, a multiple layer metal oxidecoating, a non-metal oxide coating, a metallic nitride or oxynitridecoating, a non-metallic nitride or oxynitride coating, or a multiplelayer coating comprising one or more of any of the above materials. Inone non-limiting embodiment, the first coating 50 can be a doped metaloxide coating, such as a fluorine-doped tin oxide coating, e.g. a NESA®coating commercially available from PPG Industries, Inc of Pittsburgh,Pennsylvania. An example of one suitable coating material for use as thefirst coating 50 is SUNGATE® 500 coating, which is a multilayeredtransparent conductive oxide coating commercially available from PPGIndustries, Inc of Pittsburgh, Pennsylvania and described in furtherdetail in U.S. Pat. Nos. 6,436,541. Other suitable coatings arecommercially available from PPG Industries, Inc. under the SUNGATE® andSOLARBAN® families of coatings. In another embodiment, the first coating50 can have one or more metal layers, such as described below for thesecond coating 52. The first coating 50 can be deposited by anyconventional method, such as by the methods described below for thesecond coating 52.

[0031] The first coating 50 can have any desired thickness. In oneparticular example, the first coating 50 can be a SUNGATE® 500 coatinghaving a thickness in the range of greater than 0 Å to 10,000 Å, such as500 Å to 8,000 Å, such as 2,000 Å to 6,000 Å, such as 3,000 Å to 5,000Å, such as 4,000 Å.

[0032] Contrary to conventional oven door transparencies, the secondcoating 52 can include one or more heat and/or radiation reflectivemetal layers or films comprising a reflective metal, e.g., a noble metalsuch as but not limited to gold, copper, or silver, or combinations oralloys thereof. The second coating 52 can also include one or moreanti-reflective and/or dielectric coating materials, such as metaloxides or oxides of metal alloys.

[0033] An exemplary second coating 52 is shown in FIG. 3. The secondcoating 52 can be deposited over a substrate 54 (panel) by anyconventional method, such as but not limited to conventional chemicalvapor deposition (CVD) and/or physical vapor deposition (PVD) methods.Examples of CVD processes include spray pyrolysis, chemical vapordeposition (CVD), and sol-gel deposition. Examples of PVD processesinclude electron beam evaporation and vacuum sputtering (such asmagnetron sputter vapor deposition (MSVD)). In one non-limitingembodiment, the coating 52 can be deposited by MSVD. Examples of MSVDcoating devices and methods will be well understood by one of ordinaryskill in the art and are described, for example, in U.S. Pat. Nos.4,379,040; 4,861,669; 4,898,789; 4,898,790; 4,900,633; 4,920,006;4,938,857; 5,328,768; and 5,492,750.

[0034] The illustrated exemplary second coating 52 includes a base layeror first dielectric layer 56 deposited over at least a portion of amajor surface of the substrate 54. The first dielectric layer 56 cancomprise one or more films of anti-reflective materials and/ordielectric materials, such as but not limited to metal oxides, oxides ofmetal alloys, nitrides, oxynitrides, or mixtures thereof. The firstdielectric layer 56 can be transparent to visible light. Examples ofsuitable metal oxides for the first dielectric layer 56 include oxidesof titanium, hafnium, zirconium, niobium, zinc, bismuth, lead, indium,tin, and mixtures thereof. These metal oxides can have small amounts ofother materials, such as manganese in bismuth oxide, indium in tinoxide, etc. Additionally, oxides of metal alloys or metal mixtures canbe used, such as oxides containing zinc and tin (e.g., zinc stannate),oxides of indium-tin alloys, silicon nitrides, silicon aluminumnitrides, or aluminum nitrides. Further, doped metal oxides, such asantimony or indium doped tin oxides or nickel or boron doped siliconoxides, can be used. The first dielectric layer 56 can be asubstantially single phase film, such as a metal alloy oxide film, e.g.,zinc stannate, or can be a mixture of phases composed of zinc and tinoxides or can be composed of a plurality of metal oxide films, such asthose disclosed in U.S. Pat. Nos. 5,821,001; 4,898,789; and 4,898,790.

[0035] In the illustrated exemplary embodiment, the first dielectriclayer 56 can comprise a multi-film structure having a first metal alloyoxide film 58 deposited over at least a portion of the major surface ofthe substrate 54 and a second metal oxide film 60 deposited over thefirst metal alloy oxide film 58. In one embodiment, the first dielectriclayer 56 can have a total thickness of less than or equal to 500 Å,e.g., less than or equal to 300 Å, e.g., less than or equal to 280 Å.For example, the metal alloy oxide-containing film 58 can have athickness in the range of 100 Å to 500 Å, such as 150 Å to 400 Å, e.g.,200 Å to 250 Å. The metal oxide film 60 can have a thickness in therange of 50 Å to 200 Å, such as 75 Å to 150 Å, e.g., 100 Å. In oneembodiment, the metal mixture or alloy oxide-containing film 58 can havea majority of a zinc/tin alloy oxide. The zinc/tin alloy oxide can bethat obtained from magnetron sputtering vacuum deposition from a cathodeof zinc and tin that can comprise zinc and tin in proportions of 10 wt.% to 90 wt. % zinc and 90 wt. % to 10 wt. % tin. One suitable metalalloy oxide that can be present in the film is zinc stannate. By “zincstannate” is meant a composition of Zn_(x)Sn_(1−x)O_(2−x) (Formula 1)where “x” varies in the range of greater than 0 to less than 1. Forinstance, “x” can be greater than 0 and can be any fraction or decimalbetween greater than 0 to 0.9. For example where x=⅔ Formula 1 isZn_(2/3)Sn_(1/3)O_(4/3), which is more commonly described as “Zn₂SnO₄”.A zinc stannate-containing film has one or more of the forms of Formula1 in a predominant amount in the film. The metal oxide film 60 can be azinc-containing film, such as zinc oxide. The zinc oxide film caninclude other materials to improve the sputtering characteristics of theassociated cathode, e.g., the zinc oxide can contain 0 to 20 wt. % tin,e.g., 0 to 15 wt. % tin, e.g., 0 to 10 wt. % tin.

[0036] A first heat and/or radiation reflective film or layer 62 can bedeposited over the first dielectric layer 56. The first reflective layer62 can include a reflective metal, such as but not limited to metallicgold, copper, silver, or mixtures, alloys, or combinations thereof. Thefirst reflective layer 62 can have a thickness in the range of 25 Å to300 Å, e.g., 50 Å to 300 Å, e.g., 50 Å to 150 Å, such as 70 Å to 110 Å,such as 75 Å to 100 Å, e.g., 80 Å to 90 Å. In one embodiment, the firstreflective layer 62 comprises a metallic silver layer.

[0037] A first primer film 64 can be deposited over the first reflectivelayer 62. The first primer film 64 can be an oxygen capturing material,such as titanium, that can be sacrificial during the deposition processto prevent degradation or oxidation of the first reflective layer 62during a sputtering process. The oxygen capturing material can be chosento oxidize before the material of the first reflective layer 62. In oneembodiment, the first primer film 64 can have a thickness in the rangeof 5 Å to 50 Å, e.g., 10 Å to 40 Å, e.g., 12 Å to 20 Å.

[0038] An optional second dielectric layer 66 can be deposited over thefirst reflective layer 62 (e.g., over the first primer film 64). Thesecond dielectric layer 66 can comprise one or more metal oxide or metalalloy oxide-containing films, such as those described above with respectto the first dielectric layer 56. In the illustrated embodiment, thesecond dielectric layer 66 includes a first metal oxide layer 68, e.g.,zinc oxide, deposited over the first primer film 64. A second metalalloy oxide layer 70, e.g., a zinc stannate layer, can be deposited overthe first zinc oxide layer 68. A third metal oxide layer 72, e.g.,another zinc oxide layer, can be deposited over the zinc stannate layer70 to form the multi-film layer 66. Each metal oxide layer 68, 72 of thesecond dielectric layer 66 can have a thickness in the range of about 50Å to 200 Å, e.g., 75 Å to 150 Å, e.g., 100 Å. The metal alloy oxidelayer 70 can have a thickness in the range of 100 Å to 500 Å, e.g., 200Å to 500 Å, e.g., 300 Å to 500 Å, e.g., 400 Å.

[0039] An optional second heat and/or radiation reflective layer 74 canbe deposited over the second dielectric layer 66. The second reflectivelayer 74 can include any one or more of the reflective materialsdescribed above with respect to the first reflective layer 62. Thesecond reflective layer 74 can have a thickness in the range of 25 Å to150 Å, e.g., 50 Å to 100 Å, e.g., 80 Å to 90 Å. In the illustratedembodiment, the second reflective layer 74 includes silver. In anotherembodiment, this second reflective layer 74 can be thicker than each ofthe first and third reflective layers.

[0040] An optional second primer film 76 can be deposited over thesecond reflective layer 74. The second primer film 76 can be any of thematerials described above with respect to the first primer film 64. Thesecond primer film 76 can have a thickness in the range of about 5 Å to50 Å, e.g., 10 Å to 25 Å, e.g., 12 Å to 20 Å. In the illustratedembodiment, the second primer film 76 includes titanium.

[0041] An optional third dielectric layer 78 can be deposited over thesecond reflective layer 74 (e.g., over the second primer film 76). Thethird dielectric layer 78 can also include one or more metal oxide ormetal alloy oxide-containing layers such as discussed above with respectto the first and second dielectric layers 56, 66. In the illustratedembodiment, the third dielectric layer 78 is a multi-film layer similarto the second dielectric layer 66. For example, the third dielectriclayer 78 can include a first metal oxide layer 80, e.g., a zinc oxidelayer, a second metal alloy oxide-containing layer 82, e.g., a zincstannate layer, deposited over the zinc oxide layer 80, and a thirdmetal oxide layer 84, e.g., another zinc oxide layer, deposited over thezinc stannate-containing layer 82. The metal oxide layers 80, 84 canhave thicknesses in the range of 50 Å to 200 Å, such as 75 Å to 150 Å,e.g., 100 Å. The metal alloy oxide layer 82 can have a thickness in therange of 100 Å to 500 Å, e.g., 200 Å to 500 Å, e.g., 300 Å to 500 Å,e.g., 400 Å.

[0042] The coating 52 can further include an optional third heat and/orradiation reflective layer 86 deposited over the third dielectric layer78. The third reflective layer 86 can be of any of the materialsdiscussed above with respect to the first and second reflective layers62, 74. The third reflective layer 86 can have a thickness in the rangeof 50 Å to 100 Å, e.g., 70 Å to 90 Å, e.g., 75 Å to 85 Å. In theillustrated embodiment, the third reflective layer 86 includes silver.In one embodiment, when the first, second, and/or third reflectivelayers have or contain silver, the total amount of silver for thecoating 52 can range in the amount of 29 to 44 micrograms percentimeter2 (ugm/cm²), such as 36.5 ugm/cm².

[0043] An optional third primer film 88 can be deposited over the thirdreflective layer 86. In one embodiment, the third primer film 88 can beof any of the primer materials described above. The third primer film 88can have a thickness in the range of 5 Å to 50 Å, e.g., 10 Å to 25 Å,e.g., 12 Å to 20 Å. In the illustrated embodiment, the third primer film88 is titanium.

[0044] An optional fourth dielectric layer 90 can be deposited over thethird reflective layer 86 (e.g., over the third primer film 88). Thefourth dielectric layer 90 can be comprised of one or more metal oxideor metal alloy oxide-containing layers, such as those discussed abovewith respect to the first, second, or third dielectric layers. In oneembodiment, the fourth dielectric layer 90 is a multi-film layer havinga first metal oxide layer 92, e.g., a zinc oxide layer, deposited overthe third primer film 88 and a second metal alloy oxide layer 94, e.g.,a zinc stannate layer, deposited over the zinc oxide layer 92. The metaloxide layer 92 can have a thickness in the range of 25 Å to 200 Å, suchas 50 Å to 150 Å, such as 100 Å. The metal alloy oxide layer 94 can havea thickness in the range of 25 Å to 500 Å, e.g., 50 Å to 250 Å, e.g.,100 Å to 150 Å. A suitable coating 52 for the practice of the inventionis disclosed in U.S. patent application Ser. No. 10/364,089.

[0045] The coating 52 can include a protective coating 96, e.g.,deposited over the optional fourth dielectric layer 90 (if present), toassist in providing protection against mechanical and chemical attack.The protective coating 96 can be of any desired material or mixture ofmaterials. In one exemplary embodiment, the protective coating 96 caninclude a layer having one or more metal oxide materials, such as butnot limited to, aluminum oxide, silicon oxide, or mixtures thereof. Forexample, the protective coating 96 can be a single coating layercomprising in the range of 0 wt. % to 100 wt. % alumina and/or 0 wt. %to 100 wt. % silica, such as 5 wt. % to 100 wt. % alumina and 95 wt. %to 0 wt. % silica, such as 10 wt. % to 90 wt. % alumina and 90 wt. % to10 wt. % silica, such as 15 wt. % to 90 wt. % alumina and 85 wt. % to 10wt. % silica, such as 50 wt. % to 75 wt. % alumina and 50 wt. % to 25wt. % silica, such as 50 wt. % to 70 wt. % alumina and 50 wt. % to 30wt. % silica, such as 35 wt. % to 100 wt. % alumina and 65 wt. % to 0wt. % silica, e.g., 70 wt. % to 90 wt. % alumina and 10 wt. % to 30 wt.% silica, e.g., 75 wt. % to 85 wt. % alumina and 15 wt. % to 25 wt. % ofsilica, e.g., 88 wt. % alumina and 12 wt. % silica, e.g., 65 wt. % to 75wt. % alumina and 25 wt. % to 35 wt. % silica, e.g., 70 wt. % aluminaand 30 wt. % silica, e.g., 60 wt. % to less than 75 wt. % alumina andgreater than 25 wt. % to 40 wt. % silica. Other materials, such asaluminum, chromium, hafnium, yttrium, nickel, boron, phosphorous,titanium, zirconium, and/or oxides thereof, can also be present, such asto adjust the refractive index of the coating. In one embodiment, therefractive index of the protective coating 96 can be in the range of 1to 3, such as 1 to 2, such as 1.4 to 2, such as 1.4 to 1.8.

[0046] Alternatively, the protective coating 96 can be a multi-layercoating formed by separately formed layers of metal oxide materials,such as but not limited to a bi-layer formed by one metaloxide-containing layer (e.g., a silica and/or alumina-containing firstlayer) formed over another metal oxide-containing layer (e.g., a silicaand/or alumina-containing second layer). The individual layers of themulti-layer protective coating 96 can be of any desired thickness.

[0047] The protective coating 96 can be of any desired thickness. In oneembodiment, the protective coating 96 can have a thickness in the rangeof 100 Å to 50,000 Å, such as 500 Å to 50,000 Å, e.g., 500 Å to 10,000Å, such as 100 Å to 3,000 Å, e.g., 100 Å to 2,000 Å, such as 2,000 Å to3,000 Å. In other non-limiting embodiments, the protective coating 96can have a thickness in the range of 100 Å to 10 microns, such as 101 Åto 1,000 Å, or 1,000 Å to 1 micron, or 1 micron to 10 microns, or 200 Åto 1,000 Å, or 5,000 Å to 8,000 Å. Further, the protective coating 96can be of non-uniform thickness. By “non-uniform thickness” is meantthat the thickness of the protective coating 96 can vary over a givenunit area, e.g., the protective coating 96 can have high and low spotsor areas.

[0048] In one non-limiting embodiment, the protective coating 96 cancomprise a first layer and a second layer formed over the first layer.In one specific non-limiting embodiment, the first layer can comprisealumina or a mixture or alloy comprising alumina and silica. Forexample, the first layer can comprise a silica/alumina mixture havinggreater than 5 wt. % alumina, such as greater than 10 wt. % alumina,such as greater than 15 wt. % alumina, such as greater than 30 wt. %alumina, such as greater than 40 wt. % alumina, such as 50 wt. % to 70wt. % alumina, such as in the range of 70 wt. % to 100 wt. % alumina and30 wt. % to 0 wt. % silica. In one non-limiting embodiment, the firstlayer can have a thickness in the range of greater than 0 Å to 1 micron,such as 50 Å to 100 Å, such as 100 Å to 250 Å, such as 101 Å to 250 Å,such as 100 Å to 150 Å, such as greater than 100 Å to 125 Å. The secondlayer can comprise silica or a mixture or alloy comprising silica andalumina. For example, the second layer can comprise a silica/aluminamixture having greater than 40 wt. % silica, such as greater than 50 wt.% silica, such as greater than 60 wt. % silica, such as greater than 70wt. % silica, such as greater than 80 wt. % silica, such as in the rangeof 80 wt. % to 90 wt. % silica and 10 wt. % to 20 wt. % alumina, e.g.,85 wt. % silica and 15 wt. % alumina. In one non-limiting embodiment,the second layer can have a thickness in the range of greater than 0 Åto 2 microns, such as 50 Å to 5,000 Å, such as 50 Å to 2,000 Å, such as100 Å to 1,000 Å, such as 300 Å to 500 Å, such as 350 Å to 400 Å.Suitable protective coatings 96 are described, for example, in U.S.patent application Ser. Nos. 10/007,382; 10/133,805; 10/397,001;10/422,094; 10/422,095; and 10/422,096.

[0049] Thus, the above-described exemplary conventional oven door 24utilizes two coated surfaces (e.g., No. 1 and No. 3 surfaces or No. 3and No. 4 surfaces) rather than four coated surfaces of the known art.At least one of the coatings can include a reflective metal layer toreflect heat and/or radiation.

[0050] As discussed above, the invention is not limited to use withconventional oven transparencies. An exemplary microwave oven door 100having a transparency 102 incorporating features of the invention isshown in FIG. 4. The microwave transparency 102 can be held in amicrowave oven door 100 in any conventional manner, such as by aconventional frame assembly. The transparency 102 includes a panel 104having an inner (No. 1) surface 106 and an outer (No. 2) surface 108. Acoating 110 of the invention can be deposited over at least a portion ofthe panel 104, e.g., over at least a portion of the inner (No. 1)surface 106.

[0051] The panel 104 can be of any material as described above for thepanels of the conventional convection oven. In one embodiment, the panel104 is glass.

[0052] The coating 110 can be a single layer coating or a multi-layercoating, such as described above for the first or second coatings 50,52. The coating 110 can include one or more reflective layers, e.g.,metal layers, such as described above for the coating 52. In onenon-limiting embodiment, the coating 110 includes at least one, e.g.,two or three, metallic silver reflective layers. The coating 110 canalso include an optional protective coating 112, such as described abovewith respect to the protective coating 96. In one embodiment, theprotective coating 112 can have a thickness in the range of 100 Å to 10microns, such as 1,000 Å to 9,000 Å, such as 5,000 Å to 8,000 Å. Thereflective metal layer(s) of the coating 110 can be selected to reflectmicrowave energy, which eliminates the need for the metal grid found inconventional microwave ovens. The coating 110 can provide a conductivityof less than or equal to 20 ohms per square, such as less than or equalto 10 ohms per square, such as less than or equal to 5 ohms per square.

[0053] The transparency 102 can also include an optional polymeric layer114. The polymeric layer 114 can be a polymeric coating deposited overthe coating 110 in any conventional manner, such as but not limited tobrushing, spraying, pouring, or electrocoating. Alternatively, thepolymeric layer 114 can be a polymeric sheet, e.g., a Mylar® sheet,adhered to the panel 104, e.g. adjacent the coating 110, in anyconventional manner. The polymeric layer 114 can include any polymericmaterial. The “polymeric material” can comprise one polymeric componentor can comprise a mixture of different polymeric components, such as butnot limited to one or more plastic materials, such as but not limited toone or more thermoset or thermoplastic materials. Useful thermosetcomponents include polyesters, epoxides, phenolics, and polyurethanessuch as reaction injected molding urethane (RIM) thermoset materials andmixtures thereof. Useful thermoplastic materials include thermoplasticpolyolefins such as polyethylene and polypropylene, polyamides such asnylon, thermoplastic polyurethanes, thermoplastic polyesters, acrylicpolymers, vinyl polymers, polycarbonates,acrylonitrile-butadiene-styrene (ABS) copolymers, EPDM rubber,copolymers and mixtures thereof.

[0054] Suitable acrylic polymers include copolymers of one or more ofacrylic acid, methacrylic acid and alkyl esters thereof, such as methylmethacrylate, ethyl methacrylate, hydroxyethyl methacrylate, butylmethacrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate and2-ethylhexyl acrylate. Other suitable acrylics and methods for preparingthe same are disclosed in U.S. Pat. No. 5,196,485.

[0055] Useful polyesters and alkyds can be prepared in a known manner bycondensation of polyhydric alcohols, such as ethylene glycol, propyleneglycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol,trimethylolpropane and pentaerythritol, with polycarboxylic acids suchas adipic acid, maleic acid, fumaric acid, phthalic acids, trimelliticacid or drying oil fatty acids. Examples of suitable polyester materialsare disclosed in U. S. Pat. Nos. 5,739,213 and 5,811,198.

[0056] Useful polyurethanes include the reaction products of polymericpolyols such as polyester polyols or acrylic polyols with apolyisocyanate, including aromatic diisocyanates such as4,4′-diphenylmethane diisocyanate, aliphatic diisocyanates such as1,6-hexamethylene diisocyanate, and cycloaliphatic diisocyanates such asisophorone diisocyanate and 4,4′-methylene-bis(cyclohexyl isocyanate).The term “polyurethane” as used herein is intended to includepolyurethanes as well as polyureas, and poly(urethane-ureas).

[0057] Suitable epoxy-functional materials are disclosed in U.S. Pat.No. 5,820,987.

[0058] Useful vinyl resins include polyvinyl acetyl, polyvinyl formal,and polyvinyl butyral.

[0059] The polymeric layer 114 can have any desired thickness. In onenon-limiting embodiment, the thickness can be in the range of 0.1 mm to5 mm. The polymeric material can have any desired refractive index. Inone embodiment, the polymeric material has a refractive index in therange of 1.4 to 1.7, such as 1.5 to 1.6.

[0060] An alternative coating 120 particularly useful for microwavedoors is shown in FIG. 5. The coating 120 includes a coating unit 122comprising a first dielectric layer 124, a reflective metal layer 126,and a second dielectric layer 128. The first and/or second dielectriclayers 124, 128 and the reflective metal layer 126 can be of any of thematerials described above for the dielectric layers or reflectivemetallic layers of the coating 52. In one non-limiting embodiment, thefirst and second dielectric layers 124, 128 comprise zinc stannate andthe reflective layer 126 comprises silver. The dielectric layers 124,128 and the reflective layer 126 can be of any desired thickness. In onenon-limiting embodiment, the first and/or second dielectric layers canhave thicknesses in the range of 50 Å to 500 Å, such as 360 Å to 400 Å,such as 350 Å. The reflective metal layer 126 can have a thickness inthe range of 50 Å to 150 Å, such as 75 Å to 125 Å, such as 80 Å to 100Å, such as 90 Å. A protective coating 130, such as that described abovefor the protective coating 96, can be formed over the coating 120. Thecoating 120 can include one coating unit 122 or, as shown by dashedlines in FIG. 5, can include a plurality of coating units, such as asecond coating unit 132 and a third coating unit 134, of similarstructure to the first coating unit 122.

[0061] While in the embodiment described above the transparency 102 washeld in a frame assembly, it is to be understood that the transparency102 itself could form the microwave oven door without the need for aseparate frame assembly. For example, the door hardware, e.g., hinges,handle, etc., could be connected directly to the glass transparency 102and the transparency 102 itself could form the door.

[0062] An exemplary door 140 having a transparency 142 particularlyuseful for a convection-microwave oven is shown in FIG. 6. Thetransparency 142 includes a first (inner) panel 144 and a second (outer)panel 146. The panels 144, 146 can be spaced apart in any conventionalmanner, such as by a conventional spacer assembly. The panels 144, 146can be of any of the materials described above for the previouslydescribed panels. The transparency 142 includes at least one coating148. In the broad practice of the invention, the coating 148 can be anycoating having at least one metallic layer capable of preventingmicrowave radiation passing through the transparency. For example, thecoating 148 can be similar to the coating 52 or the coating 120described above. The coating 148 can be formed on any panel surface,such as but not limited to the No. 2 surface as shown in FIG. 6.

[0063] As discussed above, conventional self-cleaning oven doors mustmeet certain industry recognized safety standards to be soldcommercially in the United States. For example, at a cleaningtemperature of 875° F. (468° C.) in the interior of the oven, theoutermost glass ply (third ply 34 in FIG. 2) should have an outersurface temperature (at the No. 6 surface) of less than 170° F. (77° C.)at an ambient air temperature of 77° F. (25° C.). In order to provideadditional cooling for the outer ply, conventional self-cleaning ovendoors typically include a vent system to allow convective flow ofambient air in the air gap between the outer two plies. The vent systemtypically includes a plurality of bottom vents 156 located along thebottom of the door and a plurality of top vents 150 located along thetop of the door (FIGS. 1, 2, and 7). During the self-cleaning cycle,ambient air flows along the flow path (shown by arrow 158 in FIG. 2)from the bottom vent(s) 156, between the outer two plies, and out of thetop vent(s) 150. This convective flow helps carry away heat from theouter surface (No. 4 surface) of the second ply, which in turn helps toreduce the temperature of the outer surface (No. 6 surface) of the outerply. However, a drawback of this conventional system is that the heatedair flowing out of the top vents 150 flows into the kitchen and, thus,increases the ambient temperature in the kitchen.

[0064] In the practice of the invention, the metal oxide or NESAcoatings of the conventional self-cleaning oven door structure arereplaced and/or substituted with one or more coatings containingreflective metal layers. FIG. 7 shows one exemplary embodiment of anoven door 160, such as a self-cleaning oven door, incorporating featuresof the invention. In this embodiment, the inner panel 30 and outer panel34 can be conventional clear glass and can be free of coatings depositedthereon. The second panel 32 has a first coating 162 that can contain atleast one metal layer. In one non-limiting embodiment, the coating 162can be positioned on the No. 3 surface. The second panel 32 can alsoinclude a second coating 164 that can contain at least one metal layerand can be positioned, for example, on the No. 4 surface. The coatings162, 164 can be the same or different and can be, for example, the sameas the coatings 50 and/or 52 described above. In one embodiment, thefirst coating 162 and/or the second coating 164 can contain one or moremetallic silver layers, such as two or more metallic silver layers, suchas three or more metallic silver layers.

[0065] As will be appreciated by one skilled in the art, during routinecleaning of the oven door 160, some of the cleaning solvent may besprayed through the vents 150, 156 (if present) and land on the coating164. This cleaning solvent could degrade or dissolve portions of thecoating 164. One option to address this problem is to apply a protectivecoating over the coating 164 to protect the coating 164 against solventattack. For example, a protective coating 96, such as a metal oxideprotective coating as described above, could be deposited over at leasta portion of the coating 164. In one embodiment, the protective coating96 can have a thickness in the range of 1,500 Å to 5,000 Å, such asgreater than 2,000 Å, such as 2,000 Å to 4,000 Å. A protective coating96 could also be applied over the coating 162. However, applying suchthick protective coatings over the coatings 162 and/or 164 means thatthe production line may have to be slowed down in order to apply theprotective coating(s), thus limiting the throughput.

[0066] Alternatively, rather than applying such thick protectivecoating(s) 96, the invention teaches that the vents 150, 156 can beeliminated or reduced in size to such an extent that-there would belittle or no chance of solvent passing through the vents (if present)and landing on the coating 164. In which case, a protective coating 96on the coating 164 could be greatly reduced in thickness, such as toless than 1,000 Å, such as less than 750 Å, such as in the range of 400Å to 600 Å, such as about 500 Å.

[0067]FIG. 8 shows an oven door 170, such as a self-cleaning oven door,of the invention in which both the inner and outer plies 30, 34 are madeof clear glass. The vents 150, 156 have been eliminated. The second ply32 has a metal oxide coating 166, such as a SUNGATE® 500 coatingcommercially available from PPG Industries, Inc., on one surface, suchas the No. 4 surface. A metal layer-containing coating 168, such as acoating containing three metallic silver layers, can be located onanother surface, such as the No. 3 surface. A thin protective coating 96such as described above can be deposited over the coating 168. In oneembodiment, the protective coating 96 can have a thickness in the rangeof 100 Å to 1,000 Å, such as 400 Å to 600 Å, such as 500 Å. While thevents 150, 156 have been eliminated, it is advantageous if the panels30, 32, 34 are not tightly sealed in the door 170 to the extent thatthey are airtight in order to prevent damage to the door when the air inthe air gaps 152, 154 is heated during operation or cleaning. Thus, airshould still be able to flow into and out of the air gaps 152, 154 (suchas around the edges of the panels in the door framework) but the largeconventional vents 150, 156 have been eliminated such that there islittle or no chance for cleaning solution to contact the outer coating166. In one embodiment the vents, if present, can have openings of lessthan 10 square inches per side of the oven door, such as less than 8square inches, such as less than 5 square inches, such as less than 3square inches.

[0068]FIG. 9 shows another embodiment of the invention in which an ovendoor 180 has four plies of glass 182, 184, 186, and 188. The first andfourth plies 182, 188 can be clear glass. The second ply 184 can have ametal layer-containing coating 190, such as described above for thecoating 52 having a protective coating 96, on a surface, such as the No.3 surface. The third ply 186 can have a metal layer-containing coating192, such as the coating 52 described above having a protective coating96, on a surface, such as the No. 5 surface or the No. 6 surface. Anoptional non-metal layer-containing coating 194, such as a SUNGATE® 500coating, can be deposited on a surface, such as the No. 6 surface if thecoating 192 is on the No. 5 surface.

[0069] Designing a self-cleaning oven door without the conventionalvents provides several advantages. For example, eliminating or reducingthe size of the vents also eliminates or reduces the requirement for theoutermost metal-containing coating to have a protective coating toprotect it against solvent attack. Since the likelihood is small thatsolvent can penetrate the redesigned door, the protective coating, suchas a metal oxide coating as described above, can be reduced from athickness of 2,000 Å to 500 Å. Additionally, the improved oven door doesnot introduce as much heat into the ambient atmosphere, such as thekitchen, since the convective flow through the vents is eliminated.Eliminating the vents also lowers the chemical durability requirementsfor the coatings, which in turn lowers the costs to make the door. Whilethe vents have been eliminated, the presence of the metallayer-containing coating provides sufficient heat reflection to meetconventional commercial requirements.

[0070] In one practice of the invention, the conventional NESA coatings,which have an emissivity of about 0.2 at 70° F. (21° C.), are replacedwith at least one metal layer-containing coating having an emissivity ofless than or equal to 0.15, such as in the range of 0.05 to 0.1, such asabout 0.08 at 70° F. (21° C.), and/or, optionally, a metal oxidecoating, such as a SUNGATE® 500 coating, having an emissivity of lessthan 0.2, such as in the range of 0.15 to 0.2 at 70° F. (21° C.).

[0071] As will be appreciated by one skilled in the art, the lower theemissivity, the better the heat reflection. The emissivity ofconventional metal oxide coatings, such as conventional NESA coatings,tends to steadily rise as the coating is heated or as the temperature ofan object perceived through the coating increases (for example in atemperature range of 200° F. to 1,200° F. (93° C. to 648° C.)). However,coatings containing metal reflective layers as taught by the invention,such as coatings including three silver-containing layers as describedabove, tend to show a much smaller rise in emissivity in thistemperature range and can even decrease in emissivity in thistemperature range. Therefore, in one non-limiting aspect, the inventionteaches providing a coated panel, such as for use in an appliancetransparency, that has a coating that provides an emissivity slope ofless than 10×10⁻⁵ per ° F. in the temperature range of 200° F. to 1,200°F. (93° C. to 648° C.), such as less than 7×10⁻⁵ per ° F., such as lessthan 5×10⁻⁵ per ° F., such as less than 3×10⁻⁵ per ° F., such as lessthan 1×10⁻⁵ per ° F. By “emissivity slope” is meant the change inemissivity over the change in temperature.

[0072] A substrate, such as a glass substrate having a metallayer-containing coating 52 and optionally a protective coating 96, canbe heat-treated before the coated panel is installed into an article.For example, the coated substrate can be tempered in conventional mannerto provide a heated-strengthened coated panel. The presence of thecoating 52 and optional protective coating 96 should not adverselyimpact upon the tempering process.

[0073] Moreover, a decorative or functional coating can be applied overall or a portion of a coated panel of the invention either before orafter heat treatment. For example, a ceramic frit can be applied overall or a portion of the coated panel before heat treatment, such astempering. Upon heating to sufficient temperatures, the ceramic frit canmelt to form banded or colored areas on the panel (shade band). In onenon-limiting embodiment, such a coated panel with a shade band formed offrit material can be incorporated into a conventional vehicletransparency, such as a conventional laminated automotive windshield.The ceramic band can be positioned between the plies of the laminatedwindshield.

[0074] A coated panel of the invention could also be processed in otherways. For example, the coated panel can have a screen printed layerapplied over at least a portion of the coating in conventional manner.The screen can form a decorative pattern. The coated panel could alsohave an electrocoat applied over all or a portion of the coated panelusing a conventional electrodeposition process.

[0075] An additional oven door 200 incorporating features of theinvention is shown in FIG. 10. The oven door 200 includes a first(innermost), e.g., monolithic, panel 202, a second composite panel 204,a third, e.g., monolithic, panel 205, and a fourth, e.g., monolithic,panel 206. The panels 202-206 can be of any of the panel materialsdescribed above and can be of any desired thickness. However, in thisaspect of the invention, at least one of the panels of the transparency200 is a composite panel, i.e., a panel formed by two or more separatesheets, e.g., glass sheets, with the adjacent surfaces of the glasssheets abutting or contacting each other so that there is no air gapbetween the sheets. In the illustrated embodiment, the second panel 204is formed by a first glass sheet 210 and a second glass sheet 212. Forexample, the monolithic panels 202, 206, 208 can have a thickness of 5mm and the glass sheets 210, 212 making up the composite panel 204 caneach have a thickness of 2.5 mm. A first coating 214 can be deposited onthe inner surface 216 of the first sheet 210 (corresponding to the No. 3surface) and a second coating 218 can be formed on the outer surface 220of the second sheet 212 (corresponding to the No. 4 surface). Anoptional third coating 222 can be deposited on another of the panels,such as the No. 5 or No. 6 surfaces.

[0076] In this aspect of the invention, one or both of the first andsecond coatings 214, 218 can be a metal layer-containing coating such asdescribed above for coating 52 and can include a protective coating 96.Alternatively, one or both of the coatings 214, 218 can be non-metallayer-containing coatings, such as described above for coating 50. Or,one coating can be a metal layer-containing coating and the othercoating can be a non-metal layer-containing coating. The composite panel204 can be positioned or adhered together with the adjacent sides of thesheets 210, 212 contacting each other so that there is no air gapbetween the sheets 210, 212.

[0077] The use of at least one composite panel in an oven transparencyprovides advantages over using only monolithic panels with coatings onboth sides. For example, each sheet of the composite panel need only becoated on one side, which means the sheet does not have to be run with acoating face down in the coater to coat the opposite side. This avoidsdamage to the bottom coating as it is moved through the coater. Theseparate sheets can then be positioned with their respective coatingsfacing outwardly to form the panel. Additionally, since the sheets needonly be coated on one side, the sheets are easier to heat treat, e.g.,temper, because it is easier for heat to enter the glass if there is aheat reflective-coating on only one side of the glass.

[0078] A vent 224 can be positioned between the third and fourth panelsas shown in FIG. 10 or, optionally, between the second and third panels.

[0079] While the above discussion focused on the practice of theinvention with oven transparencies, it should be appreciated that theinvention is not limited to the above-described exemplary uses. Forexample, a coated panel of the invention can be used in a conventionalrefrigerator door, such as a door to a commercial refrigeration cabinetused in grocery stores. The coated surface can be positioned to face theinterior of the refrigeration cabinet. The presence of a coating of theinvention as described above on the panel can help decrease condensationon the interior of the refrigerator door and help improve visibilitythrough the refrigerator door.

[0080] It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention, which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

What is claimed is:
 1. An appliance transparency, comprising: at leastone substrate; a first coating deposited over at least a portion of theat least one substrate, the first coating comprising at least onemetallic layer having a thickness in the range of 80 Å to 100 Å and/or aprotective coating; and a second coating comprising at least onemetallic layer having a thickness in the range of 80 Å to 100 Å and/or aprotective coating.
 2. The transparency of claim 1, further comprisingat least one dielectric layer.
 3. The transparency of claim 1, whereinat least one of the metallic layers includes at least one metal selectedfrom the group consisting of gold, copper, silver, aluminum, ormixtures, alloys, or combinations thereof.
 4. The transparency of claim2, wherein the at least one dielectric layer includes at least onematerial selected from metal oxides, oxides of metal alloys, doped metaloxides, nitrides, oxynitrides, and mixtures thereof.
 5. The transparencyof claim 4, wherein the at least one dielectric layer includes at leastone metal oxide selected from oxides of zinc, titanium, hafnium,zirconium, niobium, bismuth, indium, tin, and mixtures thereof.
 6. Thetransparency of claim 2, wherein the at least one dielectric layercomprises a plurality of dielectric films.
 7. The transparency of claim1, wherein the first coating comprises: a first dielectric layer; afirst metallic layer deposited over the first dielectric layer; a seconddielectric layer deposited over the first metallic layer; a secondmetallic layer deposited over the second dielectric layer; a thirddielectric layer deposited over the second metallic layer film; and athird metallic layer deposited over the third dielectric layer.
 8. Thetransparency of claim 7, wherein the first dielectric layer has athickness in the range of 300 Å to 350 Å.
 9. The transparency of claim7, wherein the first dielectric layer comprises a zinc oxide filmdeposited over a zinc stannate film.
 10. The transparency of claim 9,wherein the zinc oxide film has a thickness in the range of 50 Å to 200Å, for example 50 Å to 150 Å.
 11. The transparency of claim 9, whereinthe zinc stannate film has a thickness in the range of 150 Å to 500 Å.12. The transparency of claim 7, wherein the first metallic layer has athickness in the range of 80 Å to 90 Å.
 13. The transparency of claim 7,wherein the second dielectric layer comprises a first zinc oxide film, azinc stannate film deposited over the first zinc oxide film, and asecond zinc oxide film deposited over the zinc stannate film.
 14. Thetransparency coating of claim 13, wherein the first zinc oxide film hasa thickness in the range of 50 Å to 150 Å, the zinc stannate film has athickness in the range of 200 Å to 500 Å, and the second zinc oxide filmhas a thickness in the range of 50 Å to 150 Å.
 15. The transparency ofclaim 7, wherein the second metallic layer has a thickness in the rangeof 80 Å to 90 Å.
 16. The transparency of claim 7, wherein the thirddielectric layer comprises a first zinc oxide film, a zinc stannate filmdeposited over the first zinc oxide film, and a second zinc oxide filmdeposited over the zinc stannate film.
 17. The transparency coating ofclaim 16, wherein the zinc oxide films each have a thickness in therange of 50 Å to 150 Å.
 18. The transparency of claim 16, wherein thezinc stannate film has a thickness in the range of 200 Å to 800 Å. 19.The transparency of claim 7, wherein the third metallic layer has athickness in the range of 50 Å to 100 Å.
 20. The transparency of claim7, including a fourth dielectric layer deposited over the third metalliclayer.
 21. The transparency of claim 20, wherein the fourth dielectriclayer comprises a zinc stannate film deposited over a zinc oxide film.22. The transparency of claim 21, further comprising a protective layerdeposited over the fourth dielectric layer.
 23. The transparency ofclaim 21, wherein the zinc stannate film has a thickness in the range of50 Å to 200 Å.
 24. The transparency of claim 21, wherein the zinc oxidefilm has a thickness in the range of 50 Å to 150 Å.
 25. The transparencyof claim 7, wherein the third metallic layer is a protective layer. 26.The transparency of claim 1, wherein the first coating comprises atleast one coating unit comprising a first zinc stannate layer, ametallic layer formed over the zinc stannate layer, and a second zincstannate layer formed over the metallic layer.
 27. The transparency ofclaim 26, wherein the zinc stannate layers have thicknesses in the rangeof 300 Å to 400 Å.
 28. The transparency of claim 26, wherein themetallic layer of the first coating has a thickness in the range of 80 Åto 90 Å.
 29. The transparency of claim 1, wherein both the first andsecond coatings include a protective coating.
 30. The transparency ofclaim 29, wherein the protective coating comprises at least one metaloxide selected from titanium oxide, aluminum oxide, silicon oxide, andmixtures thereof.
 31. The transparency of claim 30, wherein theprotective coating has a thickness in the range of 100 Å to 10 microns.32. An oven transparency, comprising: a first panel defining a No. 1 anda No. 2 surface; a second panel spaced from the first panel and defininga No. 3 and a No. 4 surface; a third panel spaced from the second paneland defining a No. 5 and a No. 6 surface; a first coating deposited overat least a portion of the No. 3 surface, the first coating comprising atleast one metallic layer having a thickness in the range of 80 Å to 100Å; and a second coating deposited over at least a portion of the No. 5and/or No. 6 surfaces and comprising at least one metallic layer havinga thickness in the range of 80 Å to 100 Å.
 33. The transparency of claim33, wherein a protective coating is deposited over at least a portion ofat least one of the first and second coatings.
 34. The transparency ofclaim 33, wherein the second coating is deposited over both No. 5 and/orNo. 6 surfaces.
 35. The transparency of claim 32, wherein the first andsecond coatings are deposited by physical vapor deposition.
 36. An oventransparency, comprising: at least one composite panel comprising afirst glass sheet contacting a second glass sheet.
 37. The transparencyof claim 36, wherein the first glass sheet defines an inner surface andan outer surface, with a first coating deposited over at least a portionof the inner surface, wherein the second glass sheet defines an innersurface and an outer surface, with a second coating deposited over atleast a portion of the outer surface, and wherein the outer surface ofthe first sheet abuts the inner surface of the second sheet.
 38. Thetransparency of claim 37, wherein at least one of the first and secondcoatings is deposited by physical vapor deposition.
 39. The transparencyof claim 37, wherein at least one of the first and second coatingsincludes a metal layer.
 40. A microwave oven transparency, comprising: afirst panel; a coating deposited over at least a portion of the firstpanel, the coating comprising at least one metallic layer; and apolymeric layer located adjacent the coating.
 41. The transparency ofclaim 40, wherein the polymeric layer comprises a polymeric sheet. 42.The transparency of claim 40, wherein the coating includes a protectivecoating.
 43. The transparency of claim 40, wherein the coating furthercomprises a first metal oxide layer and a second metal oxide layer, withthe metallic layer located between the first and second metal oxidelayers.
 44. The transparency of claim 40, further including a secondpanel spaced from the first panel.
 45. An oven door, comprising: a firstpane spaced from a second pane, wherein at least one pane includes afirst coating having at least one metallic layer, the first coatinghaving an emissivity of less than or equal to 0.15 at 21° C.
 46. Theoven door as claimed in claim 45, including a second coating formed ofat least a portion of at least one of the panes.
 47. The oven door asclaimed in claim 45, wherein the first coating includes one or moremetallic silver layers.
 48. The oven door as claimed in claim 45,wherein the first coating includes at least three metallic silverlayers.
 49. The oven door as claimed in claim 45, wherein the secondcoating has an emissivity of less than 0.3 at 21° C.
 50. A self-cleaningoven door, comprising: a first pane; a second pane spaced from the firstpane; a third pane spaced from the second pane; and at least one coatingcontaining at least one metallic layer formed over at least a portion ofat least one of the panes, wherein the door is free of air vents.